1. Field of the Invention
The present invention relates to an optical system with a grating lens assembly which converges rays of light.
Grating lenses are used in optical system such as optical heads of optical disk apparatuses, in which a divergent bundle of rays of spherical waves from a coherent light source is converged upon a point, to realize compact, light, and inexpensive optical systems with reduced access times. Grating lenses are usually thinner, lighter, and more suited for mass production than conventional optical elements
2. Description of the Related Art
A grating lens functions to converge a bundle of parallel rays of only a specific wavelength upon a point. Accordingly, if the wavelength changes, the grating lens no longer converges the bundle of rays. Namely, use of a grating lens has the drawback that if the wavelength deviates from a predetermined value, an aberration occurs and/or a deviation of the focal point takes place.
A semiconductor laser is usually used as a coherent light source in an optical head of an optical disk apparatus. The wavelength of the semiconductor laser usually fluctuates in accordance with changes in the ambient temperature, which is usually not constant, and with changes in a driving current of the laser.